Name

getpriority, setpriority − get or set program scheduling priority

Syntax

#include <sys/time.h>
#include <sys/resource.h>

#define PRIO_PROCESS0/* process */
#define PRIO_PGRP1/* process group */
#define PRIO_USER2/* user id */

prio = getpriority(which, who)
int prio, which, who;

setpriority(which, who, prio)
int which, who, prio;

Description

The scheduling priority of the process, process group, or user, as indicated by which and who, is obtained with the getpriority call and set with the setpriority call. The which is one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, and who is interpreted relative to which (a process identifier for PRIO_PROCESS, process group identifier for PRIO_PGRP, and a user ID for PRIO_USER).  The prio is a value in the range −20 to 20.  The default priority is 0; lower priorities cause more favorable scheduling. 

The getpriority call returns the highest priority (lowest numerical value) enjoyed by any of the specified processes.  The setpriority call sets the priorities of all of the specified processes to the specified value.  Only the superuser may lower priorities.

Return Values

Since getpriority can legitimately return the value −1, it is necessary to clear the external variable errno prior to the call, then check it afterward to determine if a −1 is an error or a legitimate value.  The setpriority call returns 0 if there is no error or −1 if there is.

Diagnostics

The getpriority and setpriority system calls fail under the following conditions:

[ESRCH] No processes were located using the which and who values specified. 

[EINVAL] The which was not one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER. 

In addition to the errors indicated above, setpriority can fail under the following conditions:

[EPERM] A process was located, but neither its effective nor real user ID matched the effective user ID of the caller. 

[EACCES] A user other than the superuser attempted to change a process priority to a negative value. 

See Also

nice(1), fork(2), renice(8)